1 .Field of the Invention
The present invention is related to hot melt adhesive compositions; more particularly the present invention application is directed to improvements in hot melt adhesive compositions comprising low molecular weight ethylene copolymers having improved adhesive properties to a variety of substrate materials of both polar and non-polar characteristics.
2.Description of the Prior Art
As is known to the art, conventional hot melt adhesive compositions typically comprise three primary constituents; a base polymer which provides adhesion and toughness to the adhesive in its cooled state, a waxy material which acts to initiate the setting and solidification of the heated adhesive composition and to further minimize the viscosity, and a tackifying constituent which enhances the wetting and adhesion of the composition to the surfaces upon which it is applied. Ideally, a hot melt adhesive composition is useful for bonding a wide variety of substrates, including polar substrates such as metals, polycarbonates, polyesters including polyethylene terephthalate ("PET"), as well as halogenated polymer compositions, including PVC, and further, nonpolar substrates such as polyolefins, including polyethylene and polypropylene. Further, such hot melt adhesive compositions exhibit good compatibility of their individual constituents. The prior art proposes various solutions to these problems.
U.S. Pat. No. 5,037,874 to Nuttens et al. describes a compatible wax which comprises a synthetic polyethylene wax which includes incorporated carbon monoxide ("CO") terminal groups and a method for its production. The advantages cited by the reference include a novel process for the production of the synthetic polyethylene wax, and its compatibility with conventional hot melt adhesive compositions.
U.S. Pat. No. 4,601,948 to Lancaster provides adhesive compositions which are used in bonding materials utilizing high frequency radiation; the adhesives therein include ethylene/carbon monoxide copolymers and terpolymers which are cited as having melt indices of 0.5-2500, which are expected to be relatively higher weight materials.
U.S. Pat. Nos. 4,880,904 and 4,871,618 to Kinneberg provide adhesive compositions and laminated structures which consist essentially of a linear alternating polymer which is heat curable, and which is preferably of a number average molecular weight of the range of 10,000 to 30,000.
A paper entitled "Ethylene Copolymer for Adhesion to Plastics" by E. McBride and presented at an Adhesive and Sealant Council Seminar on Apr. 16, 1991 describes hot melt adhesive systems which include as the base polymer constituent various high molecular weight copolymers and terpolymers, including ethylene/carbon monoxide "E/CO", ethylene/vinyl acetate/carbon monoxide "E/VA/CO", and ethylene/acrylate/carbon monoxide "E/Ac/CO". The paper cites the need for improved waxes which exhibit compatibility with the aforementioned base polymers.
Japanese Kokai 181557 of 1991, describes compositions which are similar to those described in the McBride paper above.
While these and other prior art references provide useful hot melt adhesive compositions, there remains a continuing need for improved hot melt adhesive compositions featuring improved adhesive strength characteristics for both polar and non-polar type substrates.